This invention is related to an optical switching apparatus for use in optical networks for voice and data communications. In particular, the present invention is directed to an optical switching device having a common waveguide with improved light transmission between an input and an output side.
The growth of optical networks for voice and data communication has created a demand for high data-rate information-transfer capabilities. To enable such transfer capabilities, dense wavelength division multiplexing (DWDM) technology has been developed which allows transfer of multiple wavelength light beams over a single optical fiber enabling data transfer rates up to 40-100 Gb/s. High speed switching and routing devices comprise the core elements of the optical networks and allow dynamic control of the data traveling over the optical network. High data transmission rates impose significant demands on the functionality of the switching devices.
Optical cross-connect space division switches based on electro-optic (EO) deflection of the light beam have great potential for use in high speed optical networks. The basic requirements for such devices are the need for extremely fast switching time and the capability to handle a large number of input and output channels, e.g., up to 4000xc3x974000 by the year 2003. Reliability and cost are also important design factors for optical switching devices. Existing optical switching devices which employ signal conversion from optical into electrical and back into optical do not satisfy the anticipated requirements for such devices.
Switching matrixes having very low switching times can be designed to connect a very large number of input and output (I/O) ports. Such switches may be built from an assembly of simple digital optical switches where each can redirect one input signal into two possible output ports. However, optical cross-connect switching elements are more useful for large-scale implementations. These devices require large-scale monolithic switch arrays to perform switching functions. Although the principles used in optical cross-connect switching based on light beam deflection is well known, a robust, reliable, low cost and extendable integration process for such type of switching device is not available.
Currently, the main optical switching products on the market are based on MEMS technology, which employs rotating micro-mirrors to deflect light. However, these optical switching devices are not very reliable due to the large number of moving parts, and the limitation on the switching time caused by the mechanics of the mirrors.
There are several other optical switching technologies which have been proposed but which are still not well represented in the market due to various technological and economic difficulties. Such optical switching technologies include by way of example: the bubble switch, switches based on liquid crystals, and thermo-optic and electro-optic effects, etc. Most of these devices are still in the RandD stage. Some of these technologies, including EO switches, may be applicable for high speed, low cost, high reliability, and high I/O port count products.
Existing EO switch designs, however, require at least two paths from the switch, and a channel waveguide for each path in order to transmit a light input without divergence. Such channel waveguides require a relatively large amount of space in the switching device. As more channels are incorporated into the optical switching device, much more space for the channel waveguides is required.
Recently developed EO switch designs, described for example in the commonly assigned U.S. patent application Ser. No. 09/932,526, filed Aug. 17, 2001 allow for a plurality of EO switches to selectively direct light entering through a plurality of input ports to a plurality of output ports through a common waveguide. Since commonly used EO materials are also birefringent, the light leaving a switch may be deflected as a pair of diverging light beams. If the beams propagate across the waveguide with a divergence that is too large, only a fraction of the information from the input light may reach the output port, or the information may be received at more than one output port. To prevent birefringence from interfering with the operation of these switches, polarizing filters are sometimes incorporated into the switch.
These recently developed EO switch designs have input and output ports that are spaced along either side of the length of the common waveguide. Switching of optical signals between ports is performed by the appropriate amount of beam deflection across a common waveguide as determined by the waveguide materials. There is a need for an improved optical switch device that does not require as much space therein, such as by shortening the length of the common wave guide. There is a further need for an improved optical switch device that corrects or reduces the effect of birefringence of light transmitted from other portions of the device.
The present invention provides a common waveguide for an optical switch device with improved performance relative to known optical switching devices. In one embodiment of the present invention, the common waveguide increases the deflection of light beams across the optical switch device, allowing for more compact deflection portions or waveguides. In another embodiment of the present invention, the common waveguide corrects for birefringence in other portions of the optical switch device, allowing for greater light transmission efficiency across the device.
The present invention also provides an optical switch device having a common waveguide that improves the performance of prior optical switching devices. In one embodiment of the present invention, the optical switch device includes a common waveguide that increases the deflection of light beams across the optical switch device, allowing for more compact deflection portions or waveguides. In another embodiment of the present invention, the optical switch device includes a common waveguide that reduces the effect of birefringence in other portions of the optical switch device, allowing for greater light transmission efficiency across the device.
Embodiments of the present invention provide an optical switch for transmitting a plurality of light beams from an input to an output. In accordance with the present invention, a common waveguide is provided that has optical properties that improve the performance of the optical switch. In one embodiment, the switch has a first light deflection element at an input with a first birefringence, a second light deflection element at the output, and a waveguide having a second birefringence and optically disposed between the first and second light deflection elements. In accordance with the present invention, a light beam deflected by the first light deflection element is birefracted into two beams having a first divergence, the two beams have a second divergence in the waveguide, and the second birefringence differently refracts each of the two beams such that the magnitude of the second divergence is less than the magnitude of the first divergence. Preferably, there is no divergence of the two light beams in the waveguide.
Another embodiment of the present invention provides an optical switch for transmitting a light beam from one of a first plurality of inputs to one of a second plurality of outputs. The switch has a first plurality of light deflection elements with a first birefringence, a second plurality of light deflection element at the output, and a waveguide having a second birefringence and optically disposed between the first plurality of light deflection elements and the second plurality of light deflection elements. In accordance with the present invention, a light beam deflected by one of the first plurality of light deflection elements is birefracted into two beams having a first divergence, and the second birefringence differently refracts each of the two beams such that the magnitude of the second divergence is less than the magnitude of the first divergence.
Yet another embodiment of the present invention provides an optical switch for transmitting a light beam from an input to an output. The switch has a first light deflection element at the input with a first refractive index, a second light deflection element at the output, and a waveguide having a second refractive index and optically disposed between the first light deflection element and the second light deflection element. In accordance with the present invention, the first refractive index is greater than the second refractive index, such that a light beam deflected by the first light deflection element is further deflected by a greater amount in the waveguide.
One embodiment of the present invention provides an optical switch adapted to transmit a pair of diverging and perpendicularly polarized light beams from an input to an output. The switch includes a first waveguide having a birefringence and optically disposed between the input and the output. In accordance with the present invention, at least a portion of the waveguide has a birefringence, and the divergence of the pair of beams is birefracted into the waveguide to reduce the divergence of the beams.
In yet another embodiment of the present invention an optical switch is adapted to transmit a pair of diverging light beams from an input having a first refractive index to an output. The switch includes a waveguide having a second refractive index and optically disposed between the input and the output, where at least a portion of the waveguide has a first birefringence, and where the divergence of the pair of beams is birefracted into the waveguide to reduce the divergence of the beams.
These features together with the various ancillary provisions and features which will become apparent to those skilled in the art from the following detailed description, are attained by the optical switching apparatus and method of the present invention, preferred embodiments thereof being shown with reference to the accompanying drawings, by way of example only, wherein: